This is a U.S. national stage of application No. PCT/EP01/00561, filed on Jan. 18, 2001. Priority is claimed on that application and on the following application(s): Country: Germany, Application No.: 100 02 309.6, Filed: Jan. 20, 2000.
1. Field of the Invention
The invention relates to a method for determining the proportion of a gas component, in particular steam, in a gas mixture, using a drive-device-driven transport device for the gas mixture.
2. Description of the Related Art
To determine gas components in a gas mixture, usually sensors are used. The higher the temperature of the gas, and the more the sensors are exposed to impurities, the more fault-susceptible these sensors become.
DE 42 06 845 C2 discloses, starting from the known data of a gas mixture, determining the proportion of a gas component, for example steam, by disposing auxiliary blades on a fan for generating pressure differences, in which case, then, from the pressure difference at differing measuring points, the proportion of steam can then be concluded. Since these pressure differences are only very small, pressure difference measuring instruments must be used which have particular sensitivity and accuracy of measurement.
DE 22 59 459 discloses, in the conditioning of textiles, measuring the steam content of the mixture at regular intervals and correcting it if there is a deviation from the preset value. To measure the mixing ratio of steam and air, a fan is used in a measuring apparatus, the total pressure produced or the power consumption of the fan being determined in this measuring apparatus and this value being used to control the mixing ratio.
It is an object of the invention, with a cooking apparatus for treating foods, in a simple manner, that is to say using the existing drive apparatus and transport apparatus, to determine the proportion of a gas component, in particular steam, in the gas mixture and thus obtain an index for the moisture.
This object is achieved by the measures specified in claim 1.
In this concept of the solution, the fact is exploited that the density of the gas mixture essentially determines the output of the transport device, while the dynamic viscosity of the gas mixture is decisive for the friction losses of the transport device with the gas mixture. If the densities and/or dynamic viscosities of the gas components differ, depending on the composition of the gas mixture, a density and dynamic viscosity which are characteristic for the gas mixture result. In the inventive method, it is then only necessary to record, from appropriate tables available in the literature, the values for density and dynamic viscosity of the two components of a gas mixture in each case at specified pressure and temperature values, as a result for any desired mixing ratio of two components the resultant density and resultant dynamic viscosity of this mixture are obtained. The greater the density and dynamic viscosity of the gas mixture, the more power must a transport device apply under otherwise constant operating parameters.
A preferred use of the inventive method is that the established parameter is used as control parameter for influencing the composition of the gas mixture, in particular for moisture control of the treatment medium in apparatuses for treating foods. Since in the case of such cooking apparatuses, for example hot air steamers, the temperature in the cooking chamber is determined in any case as an essential state parameter and the atmospheric pressure is ubiquitous pressure information, the invention leads to a particularly simple substantially fault-free economic and in addition still relatively exact method for measuring the composition of the gas mixture of air and steam, and thus the moisture in the cooking apparatus.